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| Titel |
Generalized combination equations for canopy evaporation under dry and wet conditions |
| VerfasserIn |
J. P. Lhomme, C. Montes |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 3 ; Nr. 18, no. 3 (2014-03-26), S.1137-1149 |
| Datensatznummer |
250120312
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| Publikation (Nr.) |
 copernicus.org/hess-18-1137-2014.pdf |
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| Zusammenfassung |
| The formulation of canopy evaporation is investigated on the basis
of the combination equation derived from the Penman equation. All the
elementary resistances (surface and boundary layer) within the canopy are
taken into account, and the exchange surfaces are assumed to be subject to
the same vapour pressure deficit at canopy source height. This development
leads to generalized combination equations: one for completely dry canopies
and the other for partially wet canopies. These equations are rather complex
because they involve the partitioning of available energy within the canopy
and between the wet and dry surfaces. By making some assumptions and
approximations, they can provide simpler equations similar to the common
Penman–Monteith model. One of the basic assumptions of this down-grading
process is to consider that the available energy intercepted by the
different elements making up the canopy is uniformly distributed and
proportional to their respective area. Despite the somewhat unrealistic
character of this hypothesis, it allows one to retrieve the simple
formulations commonly and successfully used up to now. Numerical simulations
are carried out by means of a simple one-dimensional model of the
vegetation–atmosphere interaction with two different leaf area profiles. In
dry conditions and when the soil surface is moist (low surface resistance),
there is a large discrepancy between the generalized formulation and its
simpler Penman–Monteith form, but much less when the soil surface is dry. In
partially wet conditions, the Penman–Monteith-type equation substantially
underestimates the generalized formulation when leaves are evenly
distributed, but provides better estimates when leaves are concentrated in
the upper half of the canopy. |
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